ENTOMOSTKACA 965 



race by non-sexual reproduction as the young developed under 

 ordinary circumstances. 



In most Entomostraca the young at the time of their emersion 

 from the egg differ considerably from the parent, especially in having 

 only the thoracic portion of the body as yet developed, and in pos- 

 sessing but a small number of locomotor appendages (see fig. 720, 

 C-G) ; the visual organs, too, are frequently wanting at first. The 

 process of development, however, takes place with great rapidity, 

 the animal at each successive moult (which process is very commonly 

 repeated at intervals of a day or two) presenting some new parts, 

 and becoming more and more like its parent, which it very early 

 resembles in its power of multiplication, the female laying eggs 

 before she has attained her own full size. Even when the Entomo- 

 straca have attained their full growth, they continue to exuviate 

 their shell at short intervals during the whole of life ; and this 

 repeated moulting seems to prevent the animal from being injured, 

 or its movements obstructed, by the overgrowth of parasitic animal- 

 cules and conferva, weak and sickly individuals being frequently 

 seen to be so covered with such parasites that their motion and life 

 are soon arrested, apparently because they have not strength to cast 

 off and renew their envelopes. The process of development appears 

 to depend in some degree upon the influence of light, being retarded 

 when the animals are secluded from it ; but its rate is still more 

 influenced by heat ; and this appears also to be the chief agent that 

 regulates the time which elapses between the moultings of the adult, 

 these, in Daphnia, taking place at intervals of two days in warm 

 summer weather, whilst several days intervene between them when 

 the weather is colder. The cast shell carries with it the sheaths not 

 only of the limbs and plumes, but of the most delicate hairs and 

 setae which are attached to them. If the animal have previously 

 sustained the loss of a limb, it is generally renewed at the next naoult, 

 as in higher Crustacea. 1 



Forming part of the entomostracous group is the tribe of 

 suctorial Crustacea, 2 which for the most part live as parasites upon 

 the exterior of other animals (especially fish), whose juices they 

 imbibe by means of the peculiar proboscis-like organ which takes 

 in them the place of the jaws of other crustaceans; whilst other 

 appendages, representing the foot-jaws, are furnished with hooks, 

 by which these parasites attach themselves to the animals from 

 whose juices they derive their nutriment. Many of the suctorial 

 Crustacea bear a strong resemblance, even in their adult condition, 

 to other Entomostraca; but more commonly it is between the 

 earlier forms of the two that the resemblance is the closest, 

 most of the Suctoria undergoing such extraordinary changes in their 



1 For a systematic and detailed account of this group Dr. Baird's Natural 

 History of the British Entomostraca, published by the Bay Society in 1849, must 

 still be recommended. The numerous essays by Professor Glaus should also be 

 consulted. 



2 It is now generally recognised that these should be placed with the Copepoda, 

 which may be divided into the Eucopepoda and the Branchiura ; the former are 

 divisible into the Gnathostomata, most of which are non-parasitic, and have been 

 already described under Copepoda, and the Siphonostomata, of which Lemcsa is an 

 example. 



